<?php
$test = 
'{
    "username":"sophia",
    "event":{
        "failure":"unreset",
        "answers":{
            "question1":"{\\"answer\\":\\"{\\\\\\"pass\\\\\\":true,\\\\\\"mark\\\\\\":9,\\\\\\"totalmark\\\\\\":9,\\\\\\"value\\\\\\":\\\\\\"get full attention|establish classroom rules|teach key words & concepts|use visual aids|demonstrate|check understanding|introduce point system|give handouts|play\\\\\\"}\\",\\"state\\":\\"{\\\\\\"result\\\\\\":{\\\\\\"pass\\\\\\":true,\\\\\\"mark\\\\\\":9,\\\\\\"totalmark\\\\\\":9,\\\\\\"value\\\\\\":\\\\\\"get full attention|establish classroom rules|teach key words & concepts|use visual aids|demonstrate|check understanding|introduce point system|give handouts|play\\\\\\"}}\\"}"
        }
    },
     "event_source":"server"
}';
$obj = json_decode($test);
$obj->event->answers->question1 = json_decode($obj->event->answers->question1);
$obj->event->answers->question1->answer = json_decode($obj->event->answers->question1->answer);
$obj->event->answers->question1->state = json_decode($obj->event->answers->question1->state);
echo var_dump($obj);